The present invention relates generally to semiconductor fabrication and, more specifically, to a method of fabricating a transistor having an air gap spacer at a controlled air gap height.
A Fin-type Field Effect Transistor, also known as a FinFET, is a type of non-planar or “3D” transistor used in the design of modern processors. As in earlier, planar designs, it can be built on an SOI (silicon on insulator) substrate. However, FinFET designs also use a conducting channel that rises above the level of the insulator, creating a thin silicon structure, shaped like a fin. A gate electrode is wrapped around sidewalls of the fin such that the portion of the fin that is under the gate electrode functions as the transistor's channel, and the portions of the fin that are not under the gate electrode function as the source and drain regions. Multiple gates can be wrapped around the fin-shaped channel.
Gate electrodes of a FinFET are isolated from source and drain electrodes by a spacer material formed as a sidewall to the gate. In order to reduce capacitance between gate and source or between gate and drain, it is desirable to have a sidewall spacer material, such as air, that has a low-k value in a region of the sidewall. It can be difficult to fabricate FinFETs having such air-filled sidewalls.